The present invention relates to a technique for controlling the configuration of a main storage in a computer system, and in particular to addressing a system of main storage equipment which is divided into a plurality of storage equipment with the object of increasing the system capacity and distributing the system load.
A first technical problem of system design of main storage equipment in a computer system is how to connect main storage equipment which is lower in speed than arithmetic and logic equipment without degrading the performance of the arithmetic and logic equipment operating at high speed. As one of the techniques for solving that problem, there is a construction method of main storage referred to as main storage interleave.
According to this method, a main memory comprises a combination of multiple storage equipment which can operate independently of each other. By configuring main storage equipment in this way and making storage equipment each operating at low speed operate in parallel, the load borne by each storage equipment can be reduced and the throughput can be increased. As a result, main storage equipment which is equivalently high in speed as a whole can be obtained.
This method is described in Information Processing Handbook, Ohm Sha Ltd., May 1989, p. 260, for example. In an example described therein, n pieces of storage equipment are prepared, and a space of a main storage address (absolute address) which can be accessed from a program is divided into n. Each portion of this space is assigned to each of the storage equipment.
For ensuring the performance by using this interleave method, the absolute address space must be distributed so that the main storage area referred to by arithmetic and logic equipment may be suitable distributed among all of the storage equipment. In dividing the absolute address space, therefore, the area assignment should be chosen so that the area assignment to each storage equipment may become dense in the absolute address space.
That is to say, in order to distribute the main storage area referred to by a program, which runs on processing equipment, among each of the storage equipment, the storage area within each storage equipment is finely divided. In case two storage equipments are used, for example, the main storage area is divided into pieces each having a capacity of 2 KB and these are alternately assigned to the two storage equipments.
An example of this situation is shown in FIG. 9. In this example, the range of 0 to 2 KB of absolute address is assigned to a range of 0 to 2 KB in the area of a storage equipment (1) and the range of 2 to 4 KB of absolute address is assigned to a range of 2 to 4 KB of a storage equipment (2). Remaining portions are used as different areas of absolute address.
A second technical problem in the main storage equipment system technique is to facilitate changing the equipment configuration in a system comprising multiple storage equipment or changing capabilities of respective storage equipment. As a representative technical method with respect to this problem, there is a method using a floating address register (hereinafter referred to as FAR) as described in U.S. Pat. No. 4,280,176.
This method comprises the steps of referring to a table describing the configuration of the main storage with respect to the address (FAR translation table) which entry is provided at a fixed unit. When the main storage is to be referred to, this table is referred to in order to determine if storage equipment is assigned to that address or not, and if assigned, which equipment is assigned to the data required, and referring to the data in the corresponding storage equipment using that information. When a configuration of the storage equipment of the main storage is to be changed, the FAR translation table is to be changed and it is possible to perform manipulation such as disconnection of a part of storage equipment included in the main storage equipment or rearrangement of storage equipment to another area by manipulating the above described table.
In assigning storage equipment to absolute addresses by using the FAR method, the absolute address space must be divided by taking a unit as large as nearly a few MB because there are limitations to the capacity of the FAR translation table. Since this partitioning unit of absolute address space for FAR method is too large, the load supplied from processing equipment is not sufficiently distributed between storage equipment simply by distributing the address area between the storage equipment.
A third technical problem relating to the configuration of the main storage equipment is one relating to dynamic re-configuration of storage equipment. That is to say, it is desired to have a technique for disconnecting a part of storage equipment included in the main storage while continuing the system operation. This technique is for disconnecting storage equipment in which a defect has occurred or to perform maintenance service with respect to storage equipment. This is one of the problems in attaining non-stop continuous operation of a computer system. This concept regarding this technique are described in JP-A-58-88900.
Assuming that an area on an address space being used at the present time is located on storage equipment to be disconnected from this time forth. The above described prior technique discloses a procedure for moving that area onto a remaining storage equipment to continue the processing (hereafter referred to as dynamic re-configuration processing).
That is to say,
(1) From the area on the address space being used at the present time, a portion which must be left on the storage equipment to continue the processing in the system is extracted.
(2) Portions other than the portion extracted in (1) are saved into an external storage equipment whereby a void area having the same capacity as the portion extracted in (1) is made on the storage equipment which will remain in use.
(3) That indispensable area on the storage equipment to be disconnected is copied onto the void area on the storage equipment secured in the processing of (2) on the equipment which will continue to be used.
(4) The FAR table is changed. Storage equipment corresponding to the absolute address of the indispensable area is reassigned from the storage equipment to be disconnected before a copy operation, to the area of the storage equipment to be continuously used and which is also the destination of the copy operation.
In the storage equipment using both the above described FAR method and interleave method, the main storage configuration can be flexibly changed owing to the FAR table and the load can be distributed owing to interleave. Arrangements between the absolute address and a storage equipment are determined through a translation process consisting of two steps, i.e., translation by using the FAR table and interleave, however, addressing on the storage equipment becomes complicated. In an ordinary program using only the absolute address, it is not necessary to be conscious of this addressing complication. In the case of dynamic re-configuration of the main storage, however, two problems as described below are posed.
A first problem will now be described. In the case of dynamic reconfiguration, processing must be performed with attention to the assignment of data on storage equipment and determining which storage equipment contains an area indispensable to the system according to this data addressing. The complication in addressing results in dynamic re-configuration processing becoming complicated.
A second problem is that the number of storage equipment included in the main storage is specified by a mode that specifies the processing method of interleave and hence addressing between the absolute address and storage equipment is lost in the entire address space when the mode is switched. When the configuration of storage equipment is changed, therefore, the access of the main storage must be stopped, resulting in a problem. This problem will now be described by referring to an example described below.
It is now assumed that a system has two storage equipments and either alternative use of two storage equipments every 4 KB with interleave using address after FAR translation or use of only one storage equipment without performing interleave can be selected by a one-bit mode. Processing performed to change the configuration so as to disconnect one storage equipment from the above described system configuration and use only one remaining storage equipment will now be considered.
The moment the above described mode is so changed over that one storage equipment may be sued in this case, all correspondence relations between absolute addresses and data on the storage equipment are lost and hence the main storage data cannot be accessed correctly by the absolute address until relations between absolute addresses and the storage equipment is recovered. Therefore from the time the mode is changed over all accesses from other equipment which uses the indispensable area to the main storage must be suppressed.
For recovering this addressing, however, all of the data having half quantity of the indispensable area on the storage equipment must be copied to the storage equipment to the equipment which will continue to be used. As a result, a large quantity of data must be transferred. Depending upon the capacity of the main storage, the time required for processing extends over several hundred milliseconds to several seconds. This is a long period of suspension which cannot be permitted even in a general input/output equipment such as disk equipment or communication control equipment. This causes a problem of aggravated response in a process control system, an online control system or the like requested to work in real-time operation.